Telocytes: new insight into the pathogenesis of gallstone disease

Vascular endothelial growth factor facilitates the effects of telocytes on tumor cell proliferation and migration

Background

Telocytes, recently recognized as interstitial cells with a diverse range of potential functions, have attracted considerable attention for their involvement in tumorigenesis. Nevertheless, owing to certain challenges in the isolation and cultivation of telocytes, the research on telocytes has advanced rather slowly. Therefore, it is imperative to study the role and mechanisms of telocytes in tumors.

Methods

We improved the separation method and successfully isolated telocytes by exploiting the combination of cell adhesion and magnetic bead sorting. Telocytes conditioned medium was collected to culture tumor cells and explore the role and mechanisms of telocytes in tumors.

Results

MTT and colony formation assays demonstrated that telocytes promoted tumor cell proliferation. Wound healing experiments and transwell assays indicated that telocytes enhanced tumor cell migration. Real-time reverse transcriptase PCR analysis showed that the expression of E-cadherin was decreased, and that of Vimentin was notably increased. ELISA results revealed that telocytes secreted high levels of vascular endothelial growth factor (VEGF). And the promoting effects were alleviated by the VEGF inhibitor bevacizumab.

Conclusion

Our findings revealed that telocytes promoted tumor cell proliferation, migration, and angiogenesis through VEGF. Notably, these effects were inhibited by the addition of bevacizumab. In conclusion, our findings illuminated the role of telocytes in promoting tumor progression, and confirmed their crucial regulatory role in the growth of tumor cells.

Sphincter of Oddi Dysfunction Induces Gallstone by Inhibiting the Expression of ABCB11 via PKC-α

The abnormal increase of Oddi sphincter pressure and total bile duct pressure may play an important role in the formation of cholesterol stones, but the specific molecular mechanism is still unclear. This study aims to investigate it through in vitro and in vivo experiments. A mouse model of Oddi sphincter dysfunction was constructed by stone-inducing diet. We compared the two groups with PKC-α inhibitor GÖ6976 and PKC-α agonist thymeleatoxin. Oddi sphincter pressure and total bile duct pressure were measured. Biochemical analysis of total cholesterol, bile acid and bilirubin was then conducted. The histopathologic changes of bile duct were observed by HE staining and the ultrastructure of liver cells and surrounding tissues was observed by transmission electron microscopy. Through the above experiments, we found that the change of PKC-α expression may affect the formation process of gallstones. The relationship between PKC-α and ABCB11 was further verified by in vitro and in vivo experiments. Our results suggest that ABCB11 and PKC-α are co-expressed in the tubule membrane of hepatocytes and interact with each other in hepatocytes. The high cholesterol diet further enhances the activation of PKC-α and thus reduces the expression of ABCB11. The formation of cholesterol stones is associated with the down-regulation of ABCB11 expression in the tubule membrane of hepatocytes due to kinase signaling. This is the first study to demonstrate that sphincter of Oddi dysfunction induces gallstones through PKC-α inhibition of ABCB11 expression.

How traditional Chinese medicine can prevent recurrence of common bile duct stones after endoscopic retrograde cholangiopancreatography?

Common bile duct stones, as a type of cholelithiasis, are a benign biliary obstruction that easily acute abdominalgia, and Endoscopic Retrograde Cholangiopancreatography (ERCP) is usually the first choice for clinical treatment. However, the increasing recurrence rate of patients after treatment is troubling clinicians and patients. For the prevention of recurrence after ERCP, there is no guideline to provide a clear drug regimen, traditional Chinese medicine however has achieved some result in the treatment of liver-related diseases based on the "gut-liver-bile acid axis". On the basis of this, this article discusses the possibility of traditional Chinese medicine to prevent common bile duct stones (CBDS) after ERCP, and we expect that this article will provide new ideas for the prevention of recurrence of CBDS and for the treatment of cholelithiasis-related diseases with traditional Chinese medicine in future clinical and scientific research.

Inhibitory effect of telocyte-induced M1 macrophages on endometriosis: Targeting angiogenesis and invasion

PURPOSE

Telocytes (TCs), a novel type of stromal cells found in tissues, induce macrophage differentiation into classically activated macrophages (M1) types and enhance their phagocytic function. The purpose of this study was to investigate the inhibitory effects of TC-induced M1 macrophages on endometriosis (EMs).

METHODS

mouse uterine primary TCs and endometrial stromal cells (ESCs) were isolated and identified using double immunofluorescence staining. For the in vitro study, ESCs were treated with TC-induced M1 macrophages, and the vascular endothelial growth factor (VEGF), matrix metalloproteinase 9 (MMP9), and nuclear factor kappa B (NF-κb) genes were identified by quantitative real-time PCR (qRT-PCR) or western blotting (WB). For the in vivo study, an EMs mouse model received TC-conditioned medium (TCM) via abdominal administration, and characterized the inhibitory effects on growth (lesion weight, volume, and pathology), tissue-resident macrophages differentiation by immunostaining, angiogenic capacity (CD31 and VEGF), invasive capacity (MMP9), and NF-κb expression within EMs lesions.

RESULTS

immunofluorescent staining showed that uterine TCs expressed CD34+ and vimentin+, whereas ESCs expressed vimentin+ and cytokeratin-. At the cellular level, TC-induced M1 macrophages can significantly inhibit the expression of VEGF and MMP9 in ESCs through WB or qRT-PCR, possibly by suppressing the NF-κb pathway. The in vivo study showed that macrophages switch from the alternatively activated macrophages (M2) in untreated EMs lesions to the M1 subtype after TCM exposure. Thereby, TC-induced M1 macrophages contributed to the inhibition of EMs lesions. More importantly, this effect may be achieved by suppressing the expression of NF-κb to inhibit angiogenesis (CD31 and VEGF) and invasion (MMP9) in the tissue.

CONCLUSION

TC-induced M1 macrophages play a prevailing role in suppressing EMs by inhibiting angiogenic and invasive capacity through the NF-κb pathway, which provides a promising therapeutic approach for EMs.

Telocytes and inflammation: A review

Telocytes are a new type of interstitial cell with a diverse morphology and important functions, such as mechanical support, signal transduction, immune regulation, and tissue repair. In this paper, the origin and physiological and pathological functions of telocytes as well as their role in inflammation will be discussed, and the functions and targets of telocytes in inflammation will be fully reviewed, which may contribute to a new therapeutic strategy for inflammatory diseases in the future.

Biliary Amino Acids and Telocytes in Gallstone Disease

The role of amino acids in cholesterol gallstone formation is not known. Therefore, the aim of the study was to determine the amino acid profile in the bile of patients with and without cholecystolithiasis in relation to bile lithogenicity and telocyte numbers within the gallbladder wall. The study included 23 patients with cholecystolithiasis and 12 gallstone-free controls. The levels of free amino acids in the bile were measured, and telocytes were identified and quantified in the gallbladder muscle wall. The mean values of valine, isoleucine, threonine, methionine, phenylalanine, tyrosine, glutamic acid, serine alanine, proline and cystine were significantly higher in the study group than in the controls (p from 0.0456 to 0.000005), and the mean value of cystine was significantly lower in patients with gallstone disease than in the controls (p = 0.0033). The relationship between some of the amino acids, namely alanine, glutamic acid, proline, cholesterol saturation index (CSI) and the number of telocytes was significant (r = 0.5374, p = 0.0051; r = 0.5519, p = 0.0036; and r = 0.5231, p = 0.0071, respectively). The present study indicates a potential relationship between the altered amino acid composition of bile and the reduced number of telocytes in the gallbladder muscle wall in cholelithiasis.

Morphologies and potential roles of telocytes in nervous tissue

Structurally similar cells have been found and termed telocytes (TCs) since the first characterisation of interstitial Cajal‐like cells in 1911. TCs are a novel and peculiar interstitial cell type with a small cellular body, markedly long cell processes named telopodes and a wide distribution in numerous tissues throughout the body. Besides specific morphological characteristics and immunohistochemical profiles, TCs build three‐dimensional mixed networks through homocellular (connection to each other) and/or heterocellular contacts (connection with other cell types), interaction with extracellular matrix and their vicinity to nerve endings, and thus might play, as part of an integrated system, roles in maintaining organ/tissue function. In this mini‐review, we summarise physical properties, general characteristics and distribution of TCs in diverse organs and tissues, focusing on their potential functions in nervous tissue and current challenges in investigating TCs as a distinct cell type.

Telocytes in Cutaneous Biology: A Reappraisal

The telocytes (TCs) are novel interstitial cells that have been overlooked for a long time due to their histologic similarity to other stromal cells. TCs can be separated from the stromal cells based on their distinct immunohistochemical, ultrastructural, and molecular features. Functionally, TCs are involved in the tissue renewal, mechanical support, and immune modulation. These cells are also involved in the signal transduction either through their direct interactions with the neighboring cells or through the paracrine signaling via extracellular vesicles. TCs are damaged in several inflammatory and fibrotic conditions such as ulcerative colitis, Crohn's disease, hepatic fibrosis, psoriasis, and systemic sclerosis. The transplantation of TCs in the damaged tissue can promote tissue regeneration. Therefore, enhancing tissue TCs either by their transplantation or by promoting their survival and growth using novel medications represents novel therapeutic strategy in the future. In this review, we addressed several aspects of TCs including their origin, distribution, morphologic features, and functions. We also discussed their involvement of the cutaneous TCs in the development various pathologic conditions.

Telocytes in Cutaneous Biology: A Reappraisal

The telocytes (TCs) are novel interstitial cells that have been overlooked for a long time due to their histologic similarity to other stromal cells. TCs can be separated from the stromal cells based on their distinct immunohistochemical, ultrastructural, and molecular features. Functionally, TCs are involved in the tissue renewal, mechanical support, and immune modulation. These cells are also involved in the signal transduction either through their direct interactions with the neighboring cells or through the paracrine signaling via extracellular vesicles. TCs are damaged in several inflammatory and fibrotic conditions such as ulcerative colitis, Crohn's disease, hepatic fibrosis, psoriasis, and systemic sclerosis. The transplantation of TCs in the damaged tissue can promote tissue regeneration. Therefore, enhancing tissue TCs either by their transplantation or by promoting their survival and growth using novel medications represents novel therapeutic strategy in the future. In this review, we addressed several aspects of TCs including their origin, distribution, morphologic features, and functions. We also discussed their involvement of the cutaneous TCs in the development various pathologic conditions.

Novel insights into the pathogenic impact of diabetes on the gastrointestinal tract

Type 2 and type 1 diabetes are common endocrine disorders with a progressively increasing incidence worldwide. These chronic, systemic diseases have multiorgan implications, and the whole gastrointestinal (GI) tract represents a frequent target in terms of symptom appearance and interdependent pathophysiological mechanisms. Metabolic alterations linked with diabetic complications, neuropathy and disrupted hormone homeostasis can lead to upper and/or lower GI symptoms in up to 75% of diabetic patients, with multifactorial involvement of the oesophagus, stomach, upper and lower intestine, and of the gallbladder. On the other hand, altered gastrointestinal motility and/or secretions are able to affect glucose and lipid homeostasis in the short and long term. Finally, diabetes has been linked with increased cancer risk at different levels of the GI tract. The presence of GI symptoms and a comprehensive assessment of GI function should be carefully considered in the management of diabetic patients to avoid further complications and to ameliorate the quality of life. Additionally, the presence of gastrointestinal dysfunction should be adequately managed to improve metabolic homeostasis, the efficacy of antidiabetic treatments and secondary prevention strategies.

Identification of PDGFRα+ cells in uterine fibroids - link between angiogenesis and uterine telocytes

INTRODUCTION

Telocytes (TCs), also called interstitial Cajal-like cells (ICLC), CD34+ cells or PDGFRα+ cells (platelet-derived growth factor receptor α positive cells), a new type of cell of mesenchymal origin, were described over one decade ago. The unique nature of these cells still deserves attention from the scientific community. Telocytes make homo- and heterocellular contact with myocytes, immunocytes and nerves, have their own immunohistochemical and secretome profiles and thus might regulate local regenerative processes including angiogenesis and fibrosis. The aim of our study was to observe the missing link between angiogenesis and telocytes in leiomyoma, the most common benign tumors affecting women of reproductive age.

MATERIAL AND METHODS

We observed uterine tissue samples from leiomyoma, adjacent myometrium and unchanged tissue from patients with leiomyoma and control subjects using routine histology, histochemistry, immunofluorescence (CD117, CD31, CD34, PDGFRα, tryptase, sFlt-1) and image analysis methods.

RESULTS

The decline of the telocyte density in the foci of fibroids correlated with poor vascularization inside the leiomyoma. Moreover, the expression of sFlt-1 (anti-angiogenic-related factor) significantly increased inside a fibroid. In leiomyoma the decrease of telocyte and blood micro-vessel density was accompanied by prevalence of collagen deposits, unlike the unchanged myometrium.

CONCLUSIONS

Our results demonstrate TCs in human uterine fibroids and highlight their possible involvement in the pathogenesis of myometrial pathology in the context of angiogenesis.

Telocytes in Fibrosis Diseases: From Current Findings to Future Clinical Perspectives

Telocytes (TCs), a distinct type of interstitial (stromal) cells, have been discovered in many organs of human and mammal animals. TCs, which have unique morphological characteristics and abundant paracrine substance, construct a three-dimensional (3D) interstitial network within the stromal compartment by homocellular and heterocellular communications which are important for tissue homeostasis and normal development. Fibrosis-related diseases remain a common but challenging problem in the field of medicine with unclear pathogenesis and limited therapeutic options. Recently, increasing evidences suggest that where TCs are morphologically or numerically destructed, many diseases continuously develop, finally lead to irreversible interstitial fibrosis. It is not difficult to find that TCs are associated with chronic inflammation and fibrosis. This review mainly discusses relationship between TCs and the occurrence of fibrosis in various diseases. We analyzed in detail the potential roles and speculated mechanisms of TCs in onset and progression of systemic fibrosis diseases, as well as providing the most up-to-date research on the current therapeutic roles of TCs and involved related pathways. Only through continuous research and exploration in the future can we uncover its magic veil and provide strategies for treatment of fibrosis-related disease.

Telocytes in the Tumor Microenvironment

There are several theories explaining the communication between cells in the context of tumor development. Over the years, interactions between normal and transformed cells have been observed. Generally, all types of cells make equal contributions to the formation of the tumor microenvironment - a location of primary oncogenesis. To date, several studies have reported the role of telocytes in cancer development, and many publications have emphasized the direct and indirect involvement of telocytes in angiogenesis; signaling through the secretion of extracellular vesicles, growth factors, and bioactive molecules; fibrosis development and extracellular matrix production; tissue repair and regeneration; and immune responses. Considering the main components of the tumor microenvironment, we will discuss the features of telocytes and their possible involvement in local tissue homeostasis.

Oviductal Telocytes in Patients with Uterine Myoma

Tubal factor infertility occurs in 30–35% of infertile pairs and may be caused by impaired muscular contractility and ciliary beating as well as immunological imbalance and chronic inflammation. Newly discovered telocytes (TCs) have a wide palette of features, which play a role in oviduct physiology. We have observed tissue samples from human fallopian tubes in patients with and without uterine myoma by immunolabelling. According to the immunohistochemical co-expression of markers, it has been determined that TCs are engaged in a wide range of physiological processes, including local innervation, sensitivity to hypoxia, regulation of calcium, and sex steroid hormones balances. Due to the proximity of NOS- and ChAT-positive nerve fibers and the expression of ion channels markers, tubal TCs might be considered conductor cells. Additionally, their integration in contractions and cilia physiology in the context of fertility has been revealed. We have observed the difference in telocytes expression in the human oviduct between groups of patients and attempted to describe this population of cells specifically in the case of infertility development, a clinically relevant avenue for further studies.

Cholesterol gallstones: Focusing on the role of interstitial Cajal-like cells

Cholesterol gallstone (CG) is a common, frequent biliary system disease in China, with a complex and multifactorial etiology. Declined gallbladder motility reportedly contributes to CG pathogenesis. Furthermore, interstitial Cajal-like cells (ICLCs) are reportedly present in human and guinea pig gallbladder tissue. ICLCs potentially contribute to the regulation of gallbladder motility, and aberrant conditions involving the loss of ICLCs and/or a reduction in its pacing potential and reactivity to cholecystokinin may promote CG pathogenesis. This review discusses the association between ICLCs and CG pathogenesis and provides a basis for further studies on the functions of ICLCs and the etiologies of CG.

Telocytes Enhances M1 Differentiation and Phagocytosis While Inhibits Mitochondria-Mediated Apoptosis Via Activation of NF-κB in Macrophages

Telocytes (TCs), which are a recently discovered interstitial cell type present in various organs and tissues, perform multiple biological functions and participate in extensive crosstalk with neighboring cells. Endometriosis (EMs) is a gynecological disease characterized by the presence of viable endometrial debris and impaired macrophage phagocytosis in the peritoneal environment. Here, CD34/vimentin-positive TCs were co-cultured with RAW264.7 cells in vitro. M1/M2 differentiation-related markers were detected; phagocytosis, energy metabolism, proliferation, apoptosis, and pathway mechanisms were studied; and the mitochondrial membrane potential (ΔΨm) was measured. Furthermore, in an EMs mouse model, the differentiation of macrophages in response to treatment with TC-conditioned medium (TCM) in vivo was studied. The results showed that upon in vitro co-culture with TCM, RAW264.7 cells differentiated more toward the M1 phenotype with enhancement of phagocytosis, increase in energy metabolism and proliferation owing to reduced the loss of ΔΨm, and suppression of dexamethasone-induced apoptosis. Further, along with the activation of NF-κB, Bcl-2 and Bcl-xl, the expression of Bax, cleaved-caspase9, and cleaved-caspase3 reduced in RAW264.7 cells. In addition, the M1 subtype was found to be the dominant phenotype among tissue and peritoneal macrophages in the EMs model subjected to in vivo TCM treatment. In conclusion, TCs enhanced M1 differentiation and phagocytosis while inhibiting apoptosis via the activation of NF-κB in macrophages, which potentially inhibited the onset of EMs. Our findings provide a potential research target and the scope for developing a promising therapeutic strategy for EMs.

Identification of CD34+/PGDFRα+ Valve Interstitial Cells (VICs) in Human Aortic Valves: Association of Their Abundance, Morphology and Spatial Organization with Early Calcific Remodeling

Aortic valve interstitial cells (VICs) constitute a heterogeneous population involved in the maintenance of unique valvular architecture, ensuring proper hemodynamic function but also engaged in valve degeneration. Recently, cells similar to telocytes/interstitial Cajal-like cells described in various organs were found in heart valves. The aim of this study was to examine the density, distribution, and spatial organization of a VIC subset co-expressing CD34 and PDGFRα in normal aortic valves and to investigate if these cells are associated with the occurrence of early signs of valve calcific remodeling. We examined 28 human aortic valves obtained upon autopsy. General valve morphology and the early signs of degeneration were assessed histochemically. The studied VICs were identified by immunofluorescence (CD34, PDGFRα, vimentin), and their number in standardized parts and layers of the valves was evaluated. In order to show the complex three-dimensional structure of CD34+/PDGFRα+ VICs, whole-mount specimens were imaged by confocal microscopy, and subsequently rendered using the Imaris (Bitplane AG, Zürich, Switzerland) software. CD34+/PDGFRα+ VICs were found in all examined valves, showing significant differences in the number, distribution within valve tissue, spatial organization, and morphology (spherical/oval without projections; numerous short projections; long, branching, occasionally moniliform projections). Such a complex morphology was associated with the younger age of the subjects, and these VICs were more frequent in the spongiosa layer of the valve. Both the number and percentage of CD34+/PDGFRα+ VICs were inversely correlated with the age of the subjects. Valves with histochemical signs of early calcification contained a lower number of CD34+/PDGFRα+ cells. They were less numerous in proximal parts of the cusps, i.e., areas prone to calcification. The results suggest that normal aortic valves contain a subpopulation of CD34+/PDGFRα+ VICs, which might be involved in the maintenance of local microenvironment resisting to pathologic remodeling. Their reduced number in older age could limit the self-regenerative properties of the valve stroma.

Effect of cholesterol on in vitro cultured interstitial Cajal-like cells isolated from guinea pig gallbladders

BACKGROUND

Loss and/or dysfunction of interstitial Cajal-like cells (ICLCs) in the gallbladder may promote cholesterol gallstone formation by decreasing gallbladder motility.

AIM

To study the effect of cholesterol on the proliferation and apoptosis of ICLCs from guinea pig gallbladders.

METHODS

Guinea pig gallbladder ICLCs were isolated and cultured in vitro. The cells were exposed to cholesterol solutions at different concentrations (0, 25, 50, and 100 mg/L) for 24 h. Then, cell proliferation was detected by the CCK-8 method and the apoptosis rate was detected by flow cytometry. Further, the expression of the c-Kit protein was detected by Western blot and the expression level of c-Kit mRNA in the cells was detected by real-time quantitative PCR.

RESULTS

After ICLCs were cultured with cholesterol at concentrations of 25, 50, and 100 mg/L, the proliferation rates decreased significantly (P < 0.05), whereas the apoptosis rates increased significantly (P < 0.05). Moreover, the expression of c-Kit protein and mRNA decreased significantly (P < 0.05).

CONCLUSION

High cholesterol concentrations can inhibit the proliferation of ICLCs and promote apoptosis. This decrease in the ICLC proliferation rate might be caused by the inhibition of the stem cell factor/c-Kit signaling pathway.

The Autonomic Innervation and Uterine Telocyte Interplay in Leiomyoma Formation

The autonomic innervation of the uterus is involved in multiple pathophysiological processes in both humans and animals. Pathological conditions such as adenomyosis or inflammatory pelvic disease are usually accompanied by significant alterations in uterine innervation. In the current study, we focused on autonomic innervation of uterine fibroids, the identification of recently described interstitial cells, telocytes, and the possible interplay between these structures. In this work, uterine telocytes were identified by immunopositivity for c-kit, CD34, and PDGFRα. Nerves were revealed by immunolabeling for neuronal markers: protein gene product PGP 9.5, inducible nitric oxide synthase (iNOS), choline acetyltransferase (ChAT), and tyrosine hydroxylase (TH). The gross organization of myometrial tissue has been analyzed by routine histology. The results demonstrated that the density of iNOS and ChAT-immunopositive neurons in the uterine fibroids was higher than that in the control samples. The density of telocytes in the fibrosis foci was lower than that in the normal myometrium. Our results suggest that autonomic innervation and telocytes are involved in the microenvironment imbalance characteristic of uterine leiomyoma. Since NOS-positive nerves play an important role in oxidative stress modulation, they might lead to a decrease in the number of telocytes, which are crucial components in the pathogenesis of leiomyoma formation.

Recently Discovered Interstitial Cell Population of Telocytes: Distinguishing Facts from Fiction Regarding Their Role in the Pathogenesis of Diverse Diseases Called "Telocytopathies"

In recent years, the interstitial cells telocytes, formerly known as interstitial Cajal-like cells, have been described in almost all organs of the human body. Although telocytes were previously thought to be localized predominantly in the organs of the digestive system, as of 2018 they have also been described in the lymphoid tissue, skin, respiratory system, urinary system, meninges and the organs of the male and female genital tracts. Since the time of eminent German pathologist Rudolf Virchow, we have known that many pathological processes originate directly from cellular changes. Even though telocytes are not widely accepted by all scientists as an individual and morphologically and functionally distinct cell population, several articles regarding telocytes have already been published in such prestigious journals as Nature and Annals of the New York Academy of Sciences. The telocyte diversity extends beyond their morphology and functions, as they have a potential role in the etiopathogenesis of different diseases. The most commonly described telocyte-associated diseases (which may be best termed "telocytopathies" in the future) are summarized in this critical review. It is difficult to imagine that a single cell population could be involved in the pathogenesis of such a wide spectrum of pathological conditions as extragastrointestinal stromal tumors ("telocytomas"), liver fibrosis, preeclampsia during pregnancy, tubal infertility, heart failure and psoriasis. In any case, future functional studies of telocytes in vivo will help to understand the mechanism by which telocytes contribute to tissue homeostasis in health and disease.

Telocytes enhanced the proliferation, adhesion and motility of endometrial stromal cells as mediated by the ERK pathway in vitro

Telocytes (TCs) is special interstitial cell that have recently been identified in the female reproductive system. Endometriosis (EMs) is a benign gynecological disease whose etiology is still not fully clear. Implantation and proliferation of endometrial stromal cells (ESCs) out of the uterus are essential processes in the development of EMs. Herein, we investigate the in vitro changes of ESCs when cocultured with TCs, and the potential mechanisms involved. The current results demonstrated that, vimentin-positive/pan cytokeratin-negative ESCs, and TCs with a characteristic structure and immunophenotype (CD34/vimentin double-positive) were successfully isolated and harvested. Morphologically, direct cell-to-cell contacts were observed between TCs and ESCs. Quantitatively, TCs treatment clearly promotes the viability of ESCs, enhances cell cycle progression at G2/M phase and upregulates p-ERK1/2 and cyclin-D3 (all P < 0.05). Functionally, ESCs educated by TCs displayed significantly enhanced adhesion ability and accelerated invasion and migration capacity (all P < 0.05). However, no significant changes were found in the rate of apoptosis and in the expression of AKT signaling pathway proteins in TCs-educated ESCs (both P > 0.05). Therefore, TCs treatment obviously enhanced the in vitro motile and invasive capacity of ESCs, which were mediated by the ERK-cyclin-D3 signaling pathway, likely through direct intercellular contacts and/or juxta-paracrine effects; signaling through this axis therefore increased the likelihood of EMs. The enhanced functions of TCs-educated ESCs not only contribute to a deeper understanding of TCs, but also highlight a new concept regarding the physiopathology and therapy of EMs and associated impaired reproductive function.

Model-Based Prediction of Plasma Concentration and Enterohepatic Circulation of Total Bile Acids in Humans

Bile acids released postprandially can modify the rate and extent of lipophilic compounds' absorption. This study aimed to predict the enterohepatic circulation (EHC) of total bile acids (TBAs) in response to caloric intake from their spillover in plasma. A model for TBA EHC was combined with a previously developed gastric emptying (GE) model. Longitudinal gallbladder volumes and TBA plasma concentration data from 30 subjects studied after ingestion of four different test drinks were supplemented with literature data. Postprandial gallbladder refilling periods were implemented to improve model predictions. The TBA hepatic extraction was reduced with the high-fat drink. Basal and nutrient-induced gallbladder emptying rates were altered by type 2 diabetes (T2D). The model was predictive of the central trend and the variability of gallbladder volume and TBA plasma concentration for all test drinks. Integration of this model within physiological pharmacokinetic modeling frameworks could improve the predictions for lipophilic compounds' absorption considerably.

Telocytes role during the postnatal development of the Mongolian gerbil jejunum

Telocytes are recently categorised CD34-positive interstitial cells that comprise the cells which were previously called interstitial Cajal-like cells (ICLCs). These were detected in the stroma of various organs such as the prostate, lungs, mammary glands, liver, gallbladder, and jejunum, among others. Several functions have been proposed for telocytes, such as a supportive role in smooth muscle contraction and immune function in adult organs, and tissue organisation and paracrine signalling during development, as well as others. In the jejunum, little is known about the function of telocytes in the adult organ, or is there any information about when these cells develop or if they could have an auxiliary role in the development of the jejunum. The present study employed histological, immunohistochemical and immunofluorescence techniques on histological sections of the jejunum of Mongolian gerbil pups on two different days of postnatal development of the jejunum, covering the maturation period of the organ. By immunolabelling for CD34, it was observed that telocytes are already present in the jejunum during the first week of postnatal life and exist in close association with the developing muscularis mucosae, which are therefore TGFβ1-positive. The telocytes are still present at the end of the first month of life, and a portion of them present co-localisation with c-Kit. Fibroblast-like cells, which are exclusively c-Kit-positive, are also observed, which may indicate the presence of interstitial Cajal cells (ICCs). Finally, it can be hypothesised that a portion of the telocytes may give rise to ICCs, which are c-Kit-positive but CD34 negative.

Primary Extragastrointestinal Stromal Tumours in the Hepatobiliary Tree and Telocytes

The first decade of the twenty-first century witnessed the presence and light microscopic, immunophenotypic, and ultrastructural characterization of interstitial Cajal-like cells (coined as 'telocytes') in virtually every extragastrointestinal site of the human body by Laurentiu M. Popescu and his co-workers. Not surprisingly, stromal tumours, immunophenotypically similar to that of telocytes [CD117 (c-KIT) +/CD34 +], have also been sporadically reported outside the tubular gut (so-called extragastrointestinal stromal tumours, EGISTs), including the gall bladder, liver, and pancreas. A meticulous literature search from January 2000 to November 2015 have found 9 such case reports of EGISTs in the gall bladder, 16 in the liver, and 31 occurring in the pancreas. The site wise mean age at presentation for these tumours were reported to be 62.2 ± 16.6, 50.9 ± 20.1, and 55.3 ± 14.3 years, respectively. Six of nine EGISTs in the gall bladder were associated with gallstones. On pathological evaluation, these tumours exhibited prominent spindled cell morphology and consistent expression of CD117/c-KIT and CD34 on immunohistochemistry and variable expression of vimentin and α-smooth muscle actin. The biological behaviour of hepatic and pancreatic lesions was favourable compared to that in the gall bladder, following definitive surgery with or without imatinib therapy. While the exact pathophysiologic role played by telocytes in various organs is yet to be fully elucidated, there seems to be a direct link between these enigmatic stromal cells and pathogenesis of gallstones and origin of EGISTs, and a hope for targeted therapies. Furthermore, the possible role of telocytes in hepatic regeneration and liver fibrosis opens a new dimension for futuristic research.

Telocytes: New Players in Gallstone Disease

Cholesterol gallstone disease is highly prevalent in Western countries, particularly in women and some specific ethnic groups. The mechanisms behind the formation of gallstones are not clearly understood, but gallbladder dysmotility seems to be a key factor that triggers the precipitation of cholesterol microcrystals from supersaturated lithogenic bile.Given that newly described interstitial cells, telocytes, are present in the gallbladder and they are located in close vicinity of smooth muscle cell and neural fibers possibly interfering with gallbladder motility or contractility, authors are trying to summarize the current knowledge on the role of telocytes with respect to disturbed gallbladder function in gallstone disease.

The Cutaneous Telocytes

Telocytes (TCs) are interstitial cells found in stroma of many organs, including the skin dermis. Ultrastructurally, normal skin TCs recapitulates all the previously documented features in interstitum of other organs. Their (ultra)structural hallmark is the presence of particular shaped cellular prolongations (termed telopodes), along other features as cellular organelles representation and their distribution within cell body and its prolongations. Transmission electron microscopy (TEM) or high magnification light microscopy indicated that the particular shape of telopodes alternate characteristically thin segments (termed podomeres) and dilated segments (called podoms). A new and powerful technique, focused ion beam scanning electron microscopy (FIB-SEM), indicated that, ultrastructurally, telopodes could be either irregular ribbon-like structures, or uneven tubular-like structures. TEM images shown that podoms consists mitochondria, elements of endoplasmic reticulum and caveolae. Immunohisochemical studies on skin TCs revealed their positive expression for CD34 and PDGFRα, but for vimentin and c-kit, also. In normal dermis, TCs are involved in junctions, either homocellular (TCs-TCs), or heterocellular (TCs - other type of cells). The junctional attribute of TCs underlies their ability of forming a 3D network within dermis. Beyond the physical interactions, the connections between TCs and other cells could be also chemical, by paracrine secretion via shed vesicles as ultrastructural studies demonstrated. In normal dermis, TCs were found distributed in particular spatial relationships with other interstitial structures and/or cells: vascular structures, nerves, skin adnexa, stem cells and immune reactive cells.To date, the study of TCs was approached into two pathologic conditions: systemic sclerosis and psoriasis. In both diseases, the normal ultrastructure of TCs and also their distribution were shown to be altered. Moreover, the pattern of TCs ultrastructural changes differs in systemic sclerosis (cytoplasmic vacuolization, swollen mitochondria, lipofuscin bodies) from those appeared in psoriasis, characterized by important dystrophic changes (telopodes fragmentation, cytoplasmic disintegration, apoptotic nuclei, nuclear extrusions). Furthermore, in psoriasis, the lesional remission is (ultra)structurally displaying a recovery of dermal TCs at values similar to normal.Considering TCs ultrastructural features, their connections and spatiality in normal dermis and also their pathologic changes, TCs are credited with roles in skin homeostasis and/or pathogeny of dermatological disorders. In our opinion, further researches should be focused on identifying a specific marker for TCs and also on comprehending the pattern of their response in different dermatoses.

Telocytes in Chronic Inflammatory and Fibrotic Diseases

Telocytes are a peculiar stromal (interstitial) cell type implicated in tissue homeostasis and development, as well as in the pathophysiology of several disorders. Severe damage and reduction of telocytes have been reported during fibrotic remodeling of multiple organs in various diseases, including scleroderma, Crohn's disease, ulcerative colitis, and liver fibrosis, as well as in chronic inflammatory lesions like those of primary Sjögren's syndrome and psoriasis. Owing to their close relationship with stem cells, telocytes are also supposed to contribute to tissue repair/regeneration. Indeed, telocytes are universally considered as "connecting cells" mostly oriented to intercellular signaling. On the basis of recent promising experimental findings, in the near future, telocyte transplantation might represent a novel therapeutic opportunity to control the evolution of chronic inflammatory and fibrotic diseases. Notably, there is evidence to support that telocytes could help in preventing abnormal activation of immune cells and fibroblasts, as well as in attenuating the altered matrix organization during the fibrotic process. By targeting telocytes alone or in tandem with stem cells, we might be able to promote regeneration and prevent the evolution to irreversible tissue injury. Besides exogenous transplantation, exploring pharmacological or non-pharmacological methods to enhance the growth and/or survival of telocytes could be an additional therapeutic strategy for many disorders.

Telocytes heterogeneity: From cellular morphology to functional evidence

Telocytes (TCs), located ubiquitously in the internal organs of vertebrates, are a heterogeneous, recently described, cell population of the stromal space. Characterized by lengthy cytoplasmic extensions that can reach tens of microns and are called telopodes (Tps), TCs are difficult to see using conventional microscopes. It was the electron microscopy which led to their first identification and Popescu's team the first responsible for the reconstructions indicating TCs 'organization' in a three-dimensional (3D) network that is believed to be accountable for the complex roles of TCs. Gradually, it became increasingly evident that TCs are difficult to characterize in terms of immunophenotype and that their phenotype is different depending on the location and needs of the tissue at one time. This review discusses the growing body of evidence accumulated since TCs were discovered and highlights how the complex interplay between TCs and stem cells might be of importance for tissue engineering and regenerative medicine.

Biliary Polyunsaturated Fatty Acids and Telocytes in Gallstone Disease

It has been reported that intake of ω-3 polyunsaturated fatty acids (PUFAs) reduces the risk of coronary heart disease. It also influences bile composition, decreasing biliary cholesterol saturation in the bile of patients with gallstones. In addition to bile composition disturbances, gallbladder hypomotility must be a cofactor in the pathogenesis of cholelithiasis, as it leads to the prolonged nucleation phase. Our current knowledge about gallbladder motility has been enhanced by the study of a population of newly described interstitial (stromal) cells-telocytes (TCs). The purpose of this study was to determine whether TC loss, reported by our team recently, might be related to bile lithogenicity, expressed as cholesterol saturation index or the difference in biliary PUFA profiles in patients who suffer from cholecystolithiasis and those not affected by this disease. We determined biliary lipid composition including the fatty acid composition of the phospholipid species in bile. Thus, we investigated whether differences in biliary fatty acid profiles (ω-3 PUFA and ω-6 PUFA) in gallbladder bile may influence its lithogenicity and the quantity of TCs within the gallbladder wall. We conclude that the altered PUFA concentrations in the gallbladder bile, with elevation of ω-6 PUFA, constitute important factors influencing TC density in the gallbladder wall, being one of the possible pathophysiological components for the gallstone disease development. This study established that altered bile composition in patients with cholelithiasis may influence TC quantity within the gallbladder muscle, and we concluded that reduction in TC number may be a consequence of the supersaturated bile toxicity, while some other bile components (ω-3 PUFA, glycocholic, and taurocholic acids) may exert protective effects on TC and thus possibly influence the mechanisms regulating gallbladder and extrahepatic bile duct motility. Thus, ω-3 PUFA may represent a possible option to prevent formation of cholesterol gallstones.

Ultrastructural and immunohistochemical characteristics of telocytes in the skin and skeletal muscle of newborn rats

Telocytes (TCs) are newly described interstitial cells that might play a role in normal and pathological conditions. The aim of this study was designed to investigate its existence in the skin and skeletal muscle of one day old newborn rats and to study their ultrastructure and immunohistochemical characteristics. Ten rats (one day old newborn) were used in this study. Dorsal skin and femoral skeletal muscle samples were obtained and examined by CD117, CD34, semi-thin and ultrathin sections examination. Semi-thin sections examination revealed multiple spindle shape cells with cytoplasmic extension in the skin and in between muscle fibers. Telocytes showed positive reaction for both CD117 and CD34 immunostains. By electron microscopy these cells were spindle shaped with small cell bodies and long processes. Telocytes showed homo-cellular junctions between two adjacent telocytes and hetero-cellular junctions between telocytes and other cellular and non-cellular structures. Multiple vesicles were seen either intra-cellular or budding from the cell membrane or detached from the telocytes leaving caveolae. It could be concluded that telocytes are present in the skin and skeletal muscle of one day old newborn rats. They might play a role in pathologies and regenerative medicine due to their ability to release vesicles.

Effects of sphincter of Oddi motility on the formation of cholesterol gallstones

AIM: To investigate the mechanisms and effects of sphincter of Oddi (SO) motility on cholesterol gallbladder stone formation in guinea pigs.

METHODS: Thirty-four adult male Hartley guinea pigs were divided randomly into two groups, the control group (n = 10) and the cholesterol gallstone group (n = 24), which was sequentially divided into four subgroups with six guinea pigs each according to time of sacrifice. The guinea pigs in the cholesterol gallstone group were fed a cholesterol lithogenic diet and sacrificed after 3, 6, 9, and 12 wk. SO manometry and recording of myoelectric activity were obtained by a multifunctional physiograph at each stage. Cholecystokinin-A receptor (CCKAR) expression levels in SO smooth muscle were detected by quantitative real-time PCR (qRT-PCR) and serum vasoactive intestinal peptide (VIP), gastrin, and cholecystokinin octapeptide (CCK-8) were detected by enzyme-linked immunosorbent assay at each stage in the process of cholesterol gallstone formation.

RESULTS: The gallstone formation rate was 0%, 0%, 16.7%, and 83.3% in the 3, 6, 9, and 12 wk groups, respectively. The frequency of myoelectric activity in the 9 wk group, the amplitude of myoelectric activity in the 9 and 12 wk groups, and the amplitude and the frequency of SO in the 9 wk group were all significantly decreased compared to the control group. The SO basal pressure and common bile duct pressure increased markedly in the 12 wk group, and the CCKAR expression levels increased in the 6 and 12 wk groups compared to the control group. Serum VIP was elevated significantly in the 9 and 12 wk groups and gastrin decreased significantly in the 3 and 9 wk groups. There was no difference in serum CCK-8 between the groups.

CONCLUSION: A cholesterol gallstone-causing diet can induce SO dysfunction. The increasing tension of the SO along with its decreasing activity may play an important role in cholesterol gallstone formation. Expression changes of CCKAR in SO smooth muscle and serum VIP and CCK-8 may be important causes of SO dysfunction.

The functional morphology and role of cardiac telocytes in myocardium regeneration

Key morphological discoveries in recent years have included the discovery of new cell populations inside the heart called cardiac telocytes. These newly described cells of the connective tissue have extremely long cytoplasmic processes through which they form functionally connected three-dimensional networks that connect cells of the immune system, nerve fibers, cardiac stem cells, and cardiac muscle cells. Based on their functions, telocytes are also referred to as "connecting cells" or "nurse cells" for cardiac progenitor stem cells. In this critical review, we provide a summary of the latest research on cardiac telocytes localized in all layers of the heart - from the historical background of their discovery, through ultrastructural, immunohistochemical, and functional characterizations, to the application of this knowledge to the fields of cardiology, stem cell research, and regenerative medicine.

Comparative Analysis of Telomerase Activity in CD117⁺ CD34⁺ Cardiac Telocytes with Bone Mesenchymal Stem Cells, Cardiac Fibroblasts and Cardiomyocytes

Background:

This study characterized the cardiac telocyte (TC) population both in vivo and in vitro, and investigated its telomerase activity related to mitosis.

Methods:

Using transmission electron microscopy and a phase contrast microscope, the typical morphological features of cardiac TCs were observed; by targeting the cell surface proteins CD117 and CD34, CD117⁺CD34⁺ cardiac TCs were sorted via flow cytometry and validated by immunofluorescence based on the primary cell culture. Then the optimized basal nutrient medium for selected population was examined with the cell counting kit 8. Under this conditioned medium, the process of cell division was captured, and the telomerase activity of CD117⁺CD34⁺ cardiac TCs was detected in comparison with bone mesenchymal stem cells (BMSCs), cardiac fibroblasts (CFBs), cardiomyocytes (CMs).

Results:

Cardiac TCs projected characteristic telopodes with thin segments (podomers) in alternation with dilation (podoms). In addition, 64% of the primary cultured cardiac TCs were composed of CD117⁺CD34⁺ cardiac TCs; which was verified by immunofluorescence. In a live cell imaging system, CD117⁺CD34⁺ cardiac TCs were observed to enter into cell division in a short time, followed by an significant invagination forming across the middle of the cell body. Using a real-time quantitative telomeric-repeat amplification assay, the telomerase concentration in CD117⁺CD34⁺ cardiac TCs was obviously lower than in BMSCs and CFBs, and significantly higher than in CMs.

Conclusions:

Cardiac TCs represent a unique cell population and CD117⁺CD34⁺ cardiac TCs have relative low telomerase activity that differs from BMSCs, CFBs and CMs and thus they might play an important role in maintaining cardiac homeostasis.

Telocytes in cardiac regeneration and repair

Telocytes (TCs) are a novel type of stromal cells reported by Popescu's group in 2010. The unique feature that distinguishes TCs from other "classical" stromal cells is their extremely long and thin telopodes (Tps). As evidenced by electron microscopy, TCs are widely distributed in almost all tissues and organs. TCs contribute to form a three-dimensional interstitial network and play as active regulators in intercellular communication via homocellular/heterocellular junctions or shed vesicles. Interestingly, increasing evidence suggests the potential role of TCs in regenerative medicine. Although the heart retains some limited endogenous regenerative capacity, cardiac regenerative and repair response is however insufficient to make up the loss of cardiomyocytes upon injury. Developing novel strategies to increase cardiomyocyte renewal and repair is of great importance for the treatment of cardiac diseases. In this review, we focus on the role of TCs in cardiac regeneration and repair. We particularly describe the intercellular communication between TCs and cardiomyocytes, stem/progenitor cells, endothelial cells, and fibroblasts. Also, we discuss the current knowledge about TCs in cardiac repair after myocardial injury, as well as their potential roles in cardiac development and aging. TC-based therapy or TC-derived exosome delivery might be used as novel therapeutic strategies to promote cardiac regeneration and repair.

Telocyte implications in human pathology: An overview

Telocytes are a recently described interstitial cell population widely distributed in the stromal compartment of many organs in vertebrates, including humans. Owing to their close spatial relationship with multiple cell types, telocytes are universally considered as 'connecting cells' mostly committed to intercellular signaling by converting the interstitium into an integrated system that drives organ development and contributes to the maintenance of local tissue homeostasis. Increasing evidence indicates that telocytes may cooperate with tissue-resident stem cells to foster organ repair and regeneration, and that telocyte damage and dysfunction may occur in several disorders. The goal of this review is to provide an overview of the most recent findings concerning the implication of telocytes in a variety of pathologic conditions in humans, including heart disease, chronic inflammation and multiorgan fibrosis. Based on recent promising experimental data, there is realistic hope that by targeting telocytes alone or in tandem with stem cells, we might be able to promote organ regeneration and/or prevent irreversible end-stage organ damage in different pathologies.

The potential role of telocytes in Tissue Engineering and Regenerative Medicine

Research and ideas for potential applications in the field of Tissue Engineering (TE) and Regenerative Medicine (RM) have been constantly increasing over recent years, basically driven by the fundamental human dream of repairing and regenerating lost tissue and organ functions. The basic idea of TE is to combine cells with putative stem cell properties with extracellular matrix components, growth factors and supporting matrices to achieve independently growing tissue. As a side effect, in the past years, more insights have been gained into cell-cell interaction and how to manipulate cell behavior. However, to date the ideal cell source has still to be found. Apart from commonly known various stem cell sources, telocytes (TC) have recently attracted increasing attention because they might play a potential role for TE and RM. It becomes increasingly evident that TC provide a regenerative potential and act in cellular communication through their network-forming telopodes. While TE in vitro experiments can be the first step, the key for elucidating their regenerative role will be the investigation of the interaction of TC with the surrounding tissue. For later clinical applications further steps have to include an upscaling process of vascularization of engineered tissue. Arteriovenous loop models to vascularize such constructs provide an ideal platform for preclinical testing of future therapeutic concepts in RM. The following review article should give an overview of what is known so far about the potential role of TC in TE and RM.

Immunohistochemistry of Telocytes in the Uterus and Fallopian Tubes

The seminal work of Popescu and colleagues first demonstrated the existence of a new cell type - the telocytes. We were among the first who reported the presence of such cells in the female genital tract and performed TEM examinations, as well as immunohistochemical staining in the attempt to find a specific marker. Telocytes from rat and from the human uterus and from human fallopian tube were extensively investigated initially by comparison with interstitial cells of Cajal. Progress in telocyte research led to the identification of different subtypes suggestive for a heterogeneous telocyte population which can even coexist in the same location. As a consequence, the functions of TCs are still elusive and can be considered a versatile phenomenon that depends on a variety of conditions, including signal reception and transmission of information via extracellular vesicles or by direct intercellular contact.

Electrophysiological Features of Telocytes

Telocytes (TCs) are interstitial cells described in multiple structures, including the gastrointestinal tract, respiratory tract, urinary tract, uterus, and heart. Several studies have indicated the possibility that TCs are involved in the pacemaker potential in these organs. It is supposed that TCs are interacting with the neighboring muscular cells and their network contributes to the initiation and propagation of the electrical potentials. In order to understand the contribution of TCs to various excitability mechanisms, it is necessary to analyze the plasma membrane proteins (e.g., ion channels) functionally expressed in these cells. So far, potassium, calcium, and chloride currents, but not sodium currents, have been described in TCs in primary cell culture from different tissues. Moreover, TCs have been described as sensors for mechanical stimuli (e.g., contraction, extension, etc.). In conclusion, TCs might play an essential role in gastrointestinal peristalsis, in respiration, in pregnant uterus contraction, or in miction, but further highlighting studies are necessary to understand the molecular mechanisms and the cell-cell interactions by which TCs contribute to the tissue excitability and pacemaker potentials initiation/propagation.

The History of Telocyte Discovery and Understanding

Telocytes (TCs) are identified as a peculiar cell type of interstitial cells in various organs. The typical features of TCs from the other cells are the extending cellular process as telopodes with alternation of podomeres and podoms. Before the year of 2010, TCs were considered as interstitial Cajal-like cells because of the similar morphology and immunohistochemical features with interstitial cells of Cajal which were found more than 100 years ago and considered to be pacemakers for gut motility. Subsequently, it demonstrated that TCs were not Cajal-like cells, and thus the new name "telocyte" was proposed in 2010. With the help of different techniques, e.g., transmission electron microscopy, immunohistochemistry, or omics science, TCs have been detected in various tissues and organs from different species. The pathological role of TCs in different diseases was also studied. According to observation in situ or in vitro, TCs played a vital role in mechanical support, signaling transduction, tissue renewal or repair, immune surveillance, and mechanical sensor via establishing homo- or heterogenous junctions with neighboring cells to form 3D network or release extracellular vesicles to form juxtacrine and paracrine. This review will introduce the origin, distribution, morphology, functions, omics science, methods, and interaction of TCs with other cells and provide a better understanding of the new cell type.

Decoding Telocytes

Telocytes (TCs) are a novel type of interstitial cells, with extremely long and thin cellular prolongations termed telopodes (Tps). TCs were first identified by Popescu et al. and described their finding as "cells with telopodes." The presence of TCs has been reported in the majority of tissues and organs (for details please visit www.telocytes.com ). TCs have been ignored or overlooked for a long time due to our inability to observe these cells via a light microscopy. TCs represent a distinct cell population, different from other types of interstitial cells, based on their distinct (ultra)structure, immunophenotype, microRNA profile, gene feature, proteome signature, and secretome features. As TCs have been suggested as new cellular targets for forthcoming therapies, developing specific methods to modulate TC numbers represents an important objective.

Telocytes in Inflammatory Gynaecologic Diseases and Infertility

Women suffered with inflammatory gynecologic diseases, such as endometriosis (EMs) and acute salpingitis (AS) often complained of sub- or infertility, even in those women without obvious macroscopic anatomical pelvic abnormalities also have unexplained infertility. Generally, besides the well-known impairment of classically described oviduct cells caused by inflammatory diseases, such as the ciliated cells, fibroblasts and myofibroblasts, the involvement of the newly identified telocytes (TCs) in disease-affected oviduct tissues and potential pathophysiological roles in fertility problems remain unknown. In this chapter, TCs was investigated in rat model of EMs- and AS-affected oviduct tissues. Results showed inflammation and ischaemia-induced extensive ultrastructural damages of TCs both in cellular body and prolongations, with obvious TCs loss and interstitial fibrotic remodelling. Such in vivo pathological alterations might contribute to structural and functional abnormalities of oviduct tissue and potentially engaged in sub- or infertility. And especially, TCs connected to various activated immunocytes in both normal and diseased tissues, thus might participate in local immunoregulation (either repression or activation) and serve a possible explanation for immune-mediated pregnancy failure. Then, in vitro cell co-culture study showed that uterine TC conditioned media (TCM) can activate mouse peritoneal macrophages and subsequently trigger its cytokine secretion, thus providepreliminary evidence that, TCs are not simply innocent bystanders, but are instead potential functional players in local immunoregulatory and immunosurveillance.

Skin telocytes versus fibroblasts: two distinct dermal cell populations

It is already accepted that telocytes (TCs) represent a new type of interstitial cells in human dermis. In normal skin, TCs have particular spatial relations with different dermal structures such as blood vessels, hair follicles, arrector pili muscles or segments of sebaceous and/or eccrine sweat glands. The distribution and the density of TCs is affected in various skin pathological conditions. Previous studies mentioned the particular (ultra)structure of TCs and also their immunophenotype, miR imprint or proteome, genome or secretome features. As fibroblast is the most common intersitital cell (also in human dermis), a dedicated comparison between human skin TCs and fibroblasts (Fbs) was required to be performed. In this study, using different techniques, we document several points of difference between human dermis TCs and Fbs. By transmission electron microscopy (TEM) and scanning electron microscopy (SEM), we demonstrated TCs with their hallmark cellular prolongations - telopodes. Thus, we showed their ultrastructural distinctiveness from Fbs. By RayBio Human Cytokine Antibody Array V analyses performed on the supernatant from separately cultured TCs and Fbs, we detected the cytokine profile of both cell types, individually. Two of 79 detected cytokines - epithelial-derived neutrophil-activating peptide 78 and granulocyte chemotactic protein-2 - were 1.5 times higher in the supernatant of TCs (comparing with Fbs). On the other hand, 37 cytokines were at least 1.5 higher in Fbs supernatant (comparing with TCs), and among them six cytokines - interleukin 5, monocyte chemotactic protein-3 (MCP-3), MCP-4, macrophage inflammatory protein-3, angiogenin, thrombopoietin - being 9.5 times higher (results also confirmed by ELISA testing). In summary, using different techniques, we showed that human dermal TCs and Fbs are different in terms of ultrastructure and cytokine profile.

The failing human heart is characterized by decreased numbers of telocytes as result of apoptosis and altered extracellular matrix composition

Telocytes (TCs) are a novel type of interstitial cells only recently described. This study aimed at characterizing and quantifying TCs and telopodes (Tps) in normal and diseased hearts. We have been suggested that TCs are influenced by the extracellular matrix (ECM) composition. We used transmission electron microscopy and c-kit immunolabelling to identify and quantify TCs in explanted human hearts with heart failure (HF) because of dilated, ischemic or inflammatory cardiomyopathy. LV myectomy samples from patients with aortic stenosis with preserved ejection fraction and samples from donor hearts which could not be used for transplantation served as controls. Quantitative immunoconfocal analysis revealed that 1 mm² of the normal myocardium contains 14.9 ± 3.4 TCs and 41.6 ± 5.9 Tps. As compared with the control group, the number of TCs and Tps in HF decreased more than twofold. There were no differences between HF and control in the number of Ki67-positive TCs. In contrast, terminal deoxynucleotidyl transferase-mediated dUTP nick end labelling-positive TCs increased threefold in diseased hearts as compared to control. Significant inverse correlations were found between the amount of mature fibrillar collagen type I and the number of TCs (r = −0.84; P < 0.01) and Tps (r = −0.85; P < 0.01). The levels of degraded collagens showed a significant positive relationship with the TCs numbers. It is concluded that in HF the number of TCs are decreased because of higher rates of TCs apoptosis. Moreover, our results indicate that a close relationship exists between TCs and the ECM protein composition such that the number of TCs and Tps correlates negatively with the amount of mature fibrillar collagens and correlates positively with degraded collagens.

Telocytes in regenerative medicine

Telocytes (TCs) are a distinct type of interstitial cells characterized by a small cell body and extremely long and thin telopodes (Tps). The presence of TCs has been documented in many tissues and organs (go to http://www.telocytes.com). Functionally, TCs form a three-dimensional (3D) interstitial network by homocellular and heterocellular communication and are involved in the maintenance of tissue homeostasis. As important interstitial cells to guide or nurse putative stem and progenitor cells in stem cell niches in a spectrum of tissues and organs, TCs contribute to tissue repair and regeneration. This review focuses on the latest progresses regarding TCs in the repair and regeneration of different tissues and organs, including heart, lung, skeletal muscle, skin, meninges and choroid plexus, eye, liver, uterus and urinary system. By targeting TCs alone or in tandem with stem cells, we might promote regeneration and prevent the evolution to irreversible tissue damage. Exploring pharmacological or non-pharmacological methods to enhance the growth of TCs would be a novel therapeutic strategy besides exogenous transplantation for many diseased disorders.

Cardiac telocytes are double positive for CD34/PDGFR-α

Telocytes (TCs) are a distinct type of interstitial cells, which are featured with a small cellular body and long and thin elongations called telopodes (Tps). TCs have been widely identified in lots of tissues and organs including heart. Double staining for CD34/PDGFR-β (Platelet-derived growth factor receptor β) or CD34/Vimentin is considered to be critical for TC phenotyping. It has recently been proposed that CD34/PDGFR-α (Platelet-derived growth factor receptor α) is actually a specific marker for TCs including cardiac TCs although the direct evidence is still lacking. Here, we showed that cardiac TCs were double positive for CD34/PDGFR-α in primary culture. CD34/PDGFR-α positive cells (putative cardiac TCs) also existed in mice ventricle and human cardiac valves including mitral valve, tricuspid valve and aortic valve. Over 87% of cells in a TC-enriched culture of rat cardiac interstitial cells were positive for PDGFR-α, while CD34/PDGFR-α double positive cells accounted for 30.25% of the whole cell population. We show that cardiac TCs are double positive for CD34/PDGFR-α. Better understanding of the immunocytochemical phenotypes of cardiac TCs might help using cardiac TCs as a novel source in cardiac repair.

Telocytes in mice bone marrow: electron microscope evidence

Telocytes (TCs) are a novel type of interstitial cell of whom presence has been recently documented in many tissues and organs. However, whether TCs exists in bone marrow is still not reported. This study aims to find out TCs in mice bone marrow by using scanning electron microscope (SEM) and transmission electron microscope (TEM). SEM images showed that in mice bone marrow most of TCs have small spherical cell body (usually 4-6 μm diameter) with thin long telopodes (Tps; usually one to three). The longest Tp observed was about 70 μm, with an uneven calibre. Direct intercellular contacts exist between TCs. TEM shows mitochondria within dilations of Tps. Also, by TEM, we show the close spatial relations of Tps with blood vessels. In conclusion, this study provides ultrastructural evidence regarding the existence of TCs in mice bone marrow, in situ.